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1905] | PEIRCE & RANDOLPH—IRRITABILITY IN ALGAE 335 
the dish, in which 426 spores had escaped and attached themselves 
inthedark. There were now 1574 spores. In three hours and a half, 
therefore, after putting the dishes in the light, 948 spores had escaped 
and become fastened to the bottom, more than twice as many as had 
escaped in twenty-three and one half hours of darkness. 
That the number of spores which had escaped was far greater than 
the number which had attached themselves is shown by the other 
dish. From this dish I carefully decanted rather more than half the 
water and shook as many as possible of the loose spores into a space 
about 6™™ square. In this space a single layer of spores covered the 
whole area of 36°™™", Half the area had two layers of spores, and 
one quarter had three layers. If these spores had been spread out 
in a single layer, they would have covered an area of 63™". The 
average diameter of the spore is o.og™™. Calculating the area of 
4 spore and dividing this into 63°¢™" we find that there were about 
2623 loose spores in this area. There were many more loose spores 
than I could collect in one spot by shaking, so that the calculated 
number of practically spherical spores is none too large, though they 
could not occupy the whole of any quadrangular area. There must 
have escaped therefore at least 3400 spores during three hours and 
a half of daylight in the dish in which I had counted 348 spores, 
twenty-three and a half hours after the dish had been put in the dark. 
At least eight times as many spores had come out, therefore, in 
three and a half hours of daylight after darkness as in nearly seven 
times - long a period of darkness. 
It is to be noted that this very large number of spores (egg-cells, 
Probably fertilized) was obtained only after an abrupt change from 
Protracted darkness to full daylight. In nature, except in polar 
"egions, the darkness is never so prolonged; and nowhere in nature is 
the change from darkness to daylight so abrupt. Whatever effect 
darkness and light have upon the discharge of the gametes must be 
exhibited in maximum degree in such an experiment as I have just 
described. | 
= i, then, that light has a decided influence on the time and the 
Pea discharge of gametes (in Cystoseira) and of non-sexual spores 
ictyopteris and Dictyota). In Fucus it has long been known 
the majority of the gametes escape and fertilization takes place 
